The present invention relates to Argyranthemum intergeneric hybrid plants and methods for increased efficiency of making hybrid plants. More specifically, the present invention relates to the production of tetraploid and aneu-tetraploid Argyranthemum plants and the production of intergeneric hybrid plants derived from crossing Argyranthemum tetraploid or aneu-tetraploid plants with plants from the group Ismelia versicolor and Glebionis sp. All publications cited are hereby incorporated by reference.
A characteristic of certain plants is the ability to occasionally cross with other species, called interspecific hybridization. Interspecific hybridization has been identified in a number of species, including Argyranthemum. For example, in Argyranthemum it has been reported that many species inter-cross naturally when geographical barriers to pollination are removed (Francisco-Ortega, J., Santos-Guerra, A., Mesa-Coello, R., Gonzalez-Feria, E., and Crawford, D., Genetic resource conservation of the endemic genus Argyranthamum Sch. Bip. (Asteraceae: Anthimideae) in the Macronesian Islands, Genetic Resources and Crop Evolution, 43: 33-39 (1996)). It has been suggested that with the wide range of flower colors available in commercially bred varieties of Argyranthemum that several species of Argyranthemum were involved in the development of modern cultivars, reported by Cunneen, T. M., The Marguerite Daisy (Argyranthemum spp): developing an understanding for breeding, Ph.D. Thesis, University of Sydney Faculty of Agriculture (1996). Thus, modern cultivars are best described as Argyranthemum×hybrida. All Argyranthemum species have a diploid chromosome number of 2n=2x=18, as reported in Humphries, C. J., A revision of the Macronesian genus Argyranthemum Webb ex Schults Bip. (Compositae-Anthimideae), Bulletin of the British Museum (Natural History), Botany, 5:145-243 (1976) and Fjellheim, S., Holten Jorgensen, M., Kjos, M., Borgen, L. A molecular study of hybridization and homoploid hybrid speciation in Argyranthemum (Asteraceae) on Tenerife, the Canary Islands, Botanical Journal of the Linnean Society 159(1):19-31, 2009.
Over time plants are more accurately described and investigated by taxonomists who thereby impose changes to the generic and specific names. In the genus Glebionis there are currently two species, G. coronaria and G. segetum, according to Mabberley, D. J., Mabberley's Plant Book, Cambridge University Press, (2008). However, these species have also been historically included in Chrysanthemum and Xanthopthalmum. In the genus Ismelia there is currently only one species, I. versicolor. Historically this species has been known as Chrysanthemum carinatum, Glebionis carinatum, and Ismelia versicolor. To avoid confusion, in this application the convention of Mabberley 2008 applies where the genus Glebionis includes two species, G. coronaria and G. segetum, and the genus Ismelia includes one species, I. versicolor. 
The complexity of inheritance influences the choice of breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Backcross breeding has been used to transfer traits that follow simple Mendelian inheritance into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed back (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Pedigree breeding is used commonly for the improvement of self-pollinating crops. Two parents that possess favorable, complementary traits are crossed to produce an F1 population. An F2 population is produced by selfing one or several F1 plants. Selection of the best individuals can begin in the F2 population. Then, beginning in the F3 generation, the best individuals in the best families are selected. Replica testing of families can begin in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7 generations), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Pedigree breeding and recurrent selection breeding methods are used to develop cultivars from breeding populations. Breeding programs combine desirable traits from two or more cultivars or various broad-based sources into breeding pools from which cultivars are developed by selfing and selection of desired phenotypes. The new cultivars are evaluated to determine which have commercial potential.
Mass and recurrent selections can be used to improve populations of either self-pollinating or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, R. W., Principles of Plant Breeding, John Wiley and Sons Inc. (1960); Simmonds, N. W., Principles of Crop Improvement, Longman Group, New York, USA (1981)).
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three or more years. The best lines are candidates for new commercial cultivars. Those still deficient in a few traits can be used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, require several steps from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and/or to a common cultivar. If a single observation is inconclusive, repeated observations can provide a better estimate of its genetic worth.
Interspecific hybridization has allowed creation of new forms of plants and the transfer of desirable features from one species into another, for example, by introgression from wild species to related cultivated species. However, the ability of any two species to create viable interspecific hybrid seeds or plants is unpredictable and often has proved impossible.
Intergeneric hybridization, the crossing of two plants from different genera, is more unpredictable and improbable than interspecific hybridization because the relative genetic distance is greater between genera than between species. Only a few successful intergeneric hybrids have been reported and they are frequently only possible through human intervention and the use of embryo rescue. One form of embryo rescue is ovule culture, which involves aseptically removing the ovule from the seed and placing the ovule onto artificial media to enable the embryo to germinate and grow into a plant. In Argyranthemum, intergeneric hybrids have been reported between a female diploid A. frutescens and a male diploid G. carinatum (syn. I. versicolor) and between a female diploid A. frutescens and a male diploid G. coronaria, all developed by ovule culture (Ohtsuka, H. and Inaba, Z., Intergeneric hybridization of marguerite (Argyranthemum futescens) with annual chrysanthemum (Glebionis carinatum) and crown daisy (G. coronaria) using ovule culture, Plant Biotechnology, 25, 535-539 (2008); Ohtsuka, H. and Inaba, Z., Breeding of Argyranthemum by interspecific and intergeneric hybridization. 1. Intergeneric hybridization of Argyranthemum and Ismeria carinata (syn. Chrysanthemum carinatum), I. coronaria (syn. Chrysanthemum coronaria) through ovule culture, Journal of the Japanese Society for Horticultural Science, 72 (Suppl. 1), p. 264 (2003); Iwazaki, Y., Ueda, Y., and Yamada, H., Studies on the acquisition method of an intergeneric hybridization of Argyranthemum and Ismelia by ovule culture, Horticultural Research (Japan), 6 (Suppl. 1), p. 212 (2007)). However, the rate of efficiency (number of pollinations performed versus number of flowering plants produced) and quality of the plants produced is very low.
For example, Ohtsuka and Inaba (2008) reported that from 70 pollinations of A. frutescens×G. carinatum (syn. I. versicolor), only 16 embryos were obtained and germinated via ovule culture, and of those only five flowering plants developed. These five plants had similar morphology to G. carinatum (syn. I. versicolor). However, two died after flowering and the remaining three had pale green foliage, indicating weak growth. Ohtsuka and Inaba (2008) also reported that from 61 pollinations of A. frutescens×G. coronaria, only 26 embryos were obtained and germinated via ovule culture, and of those only 16 flowering plants developed. These 16 plants were generally characterized by upright vigorous growth with few branches, and pale green foliage with white or white/yellow ray floret color. Ohtsuka and Inaba (2008) further explain that from this cross combination “we were unable to find novel characteristics that might be valuable for flowerbed and pot plant production.”
The present invention yielded the surprising discovery that commercially useful progeny could be developed from cross combinations using a female plant selected from the group Ismelia versicolor and Glebionis sp. crossed with a male Argyranthemum aneu-tetraploid plant. These crosses, in addition to being successful for Ismelia versicolor, Glebionis coronaria and Glebionis segetum, also surprisingly caused the female parents to self pollinate. Considering all of these species exhibit self-incompatibility (Anderson, N. O., Liedl, B. E., Ascher, P. D., Widmer R. E., and Desborough, S. L. (1988), Evaluating self-incompatibility in Chrysanthemum, Sexual Plant Reproduction 1: 173-181), it appears the stigmatic incompatability mechanism was overcome by the application of Argyranthemum pollen.
The present invention was unexpected because under conditions of intergeneric hybridization it is common to experience unilateral incongruity (Liedl, B and Anderson, N (1993). Reproductive barriers: Identification, uses and circumvention. In: Plant Breeding Reviews, 11: 11-154). That is to say, the cross will work in one direction, but not in the reciprocal. The reasons for this phenomenon can include various types of incompatibilities, and differences in endosperm balance number. In addition to useful intergeneric hybrid progeny, a large number of selfed progeny were produced by the act of pollinating the female Glebionis sp. and I. versicolor flowers with Argyranthemum pollen. This phenomenon has not been previously reported within the genera herein described.
The present invention provides another avenue for creating novel intergeneric hybrid plants and could assist in the development of such characteristics as increased capitula diameter, male sterility, female sterility, improved heat tolerance, perpetual flowering, new flower colours and brighter flower colours. Prior to the present invention, there have been no previous reports of successful hybridization at any ploidy level for plants from the group Ismelia versicolor and Glebionis sp. used as female parents crossed with Argyranthemum plants as male parents.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.